1. Field of the Invention
The present invention relates to airway pressure support systems, and, more particularly, to humidifiers provided in airway pressure support systems.
2. Description of the Related Art
Many individuals suffer from disordered breathing during sleep. Sleep apnea is a common example of such sleep disordered breathing suffered by millions of people throughout the world. One type of sleep apnea is obstructive sleep apnea (OSA), which is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstruction of the airway; typically the upper airway or pharyngeal area. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles which stabilize the upper airway segment, thereby allowing the tissues to collapse the airway. Another type of sleep apnea syndrome is a central apnea, which is a cessation of respiration due to the absence of respiratory signals from the brain's respiratory center. An apnea condition, whether OSA, central, or mixed, which is a combination of OSA and central, is defined as the complete or near cessation of breathing, for example a 90% or greater reduction in peak respiratory airflow.
Those afflicted with sleep apnea experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of sleep apnea include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete or nearly complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction of the airway typically results in shallow breathing referred to as a hypopnea. A hypopnea is typically defined as a 50% or greater reduction in the peak respiratory air-flow. Other types of sleep disordered breathing include, without limitation, upper airway resistance syndrome (UARS) and vibration of the airway, such as vibration of the pharyngeal wall, commonly referred to as snoring. Thus, in diagnosing a patient with a breathing disorder, such as OSA, central apneas, or UARS, it is important to detect accurately the occurrence of apneas and hypopneas of the patient.
It is well known to treat sleep disordered breathing by applying a positive air pressure (PAP) to the patient's airway. This positive pressure effectively “splints” the airway, thereby maintaining an open passage to the lungs. In one type of PAP therapy, known as continuous positive air pressure (CPAP), the pressure of gas delivered to the patient is constant throughout the patient's breathing cycle. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, or varies with the patient's effort, to increase the comfort to the patient. This pressure support technique is referred to as bi-level pressure support, in which the inspiratory positive airway pressure (IPAP) delivered to the patient is higher than the expiratory positive airway pressure (EPAP).
Humidifiers are frequently provided between or integral with a PAP machine and the user interface in order to humidify the otherwise relatively-dry compressed air generated by the PAP machine. Typically, humidifiers can be categorized as passover types or non-passover types. In a passover type of humidifier, water is contained in a reservoir that may or may not be heated. While the water is allowed to evaporate to produce vapor within the reservoir, breathing gas is passed over the surface of the water.
In current PAP machines, during misuse conditions, such as when the PAP machine is dropped or is rotated, water from the reservoir can enter the main housing of the PAP machine and potentially cause damage thereto. Furthermore, to account for this potential of water ingress back into the main housing of the PAP machine, the reservoir needs to be larger than what is required to deliver therapy, so that there is always sufficient water for humidification. This adds weight to the PAP machine and makes it more difficult to transport.
There is thus room for improvement in airway pressure support systems including humidifiers.